If you’re ever in the office of Nossi Gross leader of the Baltimore-based Zemer Orchestra don’t look at his calendar. Ever since he formed his band 25 years ago many entries are marked “UNOFFICIAL” in big capital letters — simchahs he’s been asked to play at that are not yet public knowledge. Mr. Gross labels these dates to remind himself to keep his lips sealed; he won’t even share the good news with his wife Rona unless he has the customer’s permission.

One popular secret occasion is a surprise engagement. “A young man called me to come with one or two musicians toQuarryLake a man-made lake inBaltimoresurrounded by residential developments and shops” relates Mr. Gross. “He planned to walk around the lake and propose on the other side. After she accepted his proposal he would send a quick text to signal his friend who was waiting to set off fireworks on the other side of the lake. I was set up not far from where he proposed — around a bend — with my flute and two other musicians an acoustic guitarist and a percussionist next to a table set with candles champagne and flowers. The surprise was pulled off beautifully and we played ‘Od Yeshama ’ ‘Siman Tov U’Mazel Tov’ and soft music while they celebrated their spanking new engagement. We were the first to see them after they were engaged.”

Sometimes the surprise doesn’t happen until the wedding day. “I’ve been asked to help pull off wedding shtick” continues Mr. Gross. “One father of a kallah rented a really expensive bird costume for an inside joke about his friend Melvin who flew in unexpectedly to join the simchah. I played Lipa Schmeltzer’s song ‘Mizrach’ while he did his favorite dance for his daughter.”

Even if requests like these seem unimportant Mr. Gross notes they mean a great deal to the chassan and kallah. Unfortunately as hard as he tries to keep the secret slipups can happen. “It’s impossible to anticipate everything. You need a lot of siyata d’Shmaya to always get it right.”